1. Field of the Invention
The present invention generally relates to a seat belt warning apparatus that generates an alert sound to alert, or remind, a vehicle occupant that his or her seat belt is unbuckled. More specifically, it relates to the same apparatus configured to generate the alert sound in a different way depending upon each warning level, and a method corresponding to the operation of such an apparatus.
2. Description of the Related Art
One known system (see U.S. Pat. No. 6,278,358) triggers an alert sound in two steps to remind an occupant that his or her seat belt is unbuckled depending upon the vehicle speed. Typically, a waning system of this kind starts up when the ignition is turned on, and determines the seat belt to be in the buckled condition in response to a corresponding seat belt buckle switch turning on. With such a system, therefore, the alert sound sounds from the ignition turning on until the seat belt buckle switch turning on.
The above audible alert triggered upon starting up the vehicle is generally called “a primary audible alert”, and one related US regulation prohibits that such an alert lasts longer than 8 seconds. The system disclosed in the above publication is arranged to cope with this requirement, which monitors, after provision of the primary audible alert, the vehicle speed and triggers a secondly audible alert in response to the vehicle starting running.
With this system, however, if a different alert sound is used for each audible alert (i.e., primary audible alert, secondary audible alert), the occupant may not realize that the secondary audible alert is alerting him or her that his or her seat belt is unbuckled due to other audible indications indicating the headlight still remaining “ON”, etc. This situation is more likely when the primary audible alert is deactivated within 8 seconds as required in the above-stated US regulation, because there is a time period of no alert (i.e., alert sound) from the end of the primary audible alert to the beginning of the secondary audible alert.
It is true that the occupant can easily associate both the primary and secondary audible alerts with the unbuckled seat belt if the same alert sound is generated in the same way for each alert. This would however make it impossible to provide a classified alert system capable of producing a higher warning level alert when the vehicle is running than when the vehicle is stationary. Also, it should be appreciated that, if the same alert sound is generated in the same way during the primary audible alert as the secondary audible alert that is a relatively strong warning, that excessively strong primary audible alert may annoy the occupant because it is activated almost every time he or she starts the vehicle.
Thus, it is difficult to achieve such a classified seat belt alert system which assures the occupant's correct recognition of each audible alert.